1. Field of the Invention
The present invention relates to an optimization method of optimally setting an emphasis and an optimization device for optimally setting an emphasis. In particular, the invention relates to an emphasis optimization device and an emphasis optimization method, in which a transmission path (excluding active devices) including various kinds of passive devices, for example, cables, connectors, filters, fixed attenuators, and the like is targeted, and through which it is possible to optimize an emphasis setting value added to a digital signal to be transmitted on the transmission path (the target system).
2. Description of the Related Art
In recent years, as digital communication increases in speed, ultrahigh-speed digital signals, for example, having a transmission rate of 25 Gbit/s, are commonly transmitted on the high-speed connectors connecting printed-circuit boards (PCBs) or platforms.
However, in the case where the ultrahigh-speed digital signals of a transmission rate of 25 Gbit/s as described above are transmitted on the transmission paths such as the PCBs and the high-speed connectors, an error may occur as the transmission path is lengthened. Further, transmission loss may occur due to the deficiency in the transmission bandwidth and thus the distortion of waveforms becomes large. Therefore, there is a problem in that the communication qualities are degraded. In recent years, as a solution for improving the communication qualities, an emphasis is added to the digital signal.
For example, as a method of generating an emphasis to be added to the digital signal, Jpn. Pat. Appln. KOKAI Publication No. 2008-271552 discloses an adaptive pre-emphasis device and the method thereof. In the device and the method disclosed in the KOKAI Publication No. 2008-271552, an input file including digital data representing a digital-data-pattern waveform is received and is subjected to pre-emphasis process. This pre-emphasis process comprises up-sampling the digital data at a rate of Fs/Fd, generating a step response using the up-sampled digital data, differentiating the generated step response, generating a pre-emphasis•filtering coefficient, convolving the coefficient and the received digital-data-pattern waveform input signal, and generating a pre-emphasized digital-data-pattern. According to the method, it is realized that the signals pre-emphasized by various kinds of data generating devices are generated.
However, even in a case of the above-mentioned pre-emphasis or a de-emphasis, the level of the quality improvement achieved by adding the emphasis to the digital signal varies greatly depending on a tap width and an intensity value (a modulation depth) for every tap.
By the way, in a case where the emphasis is added to the digital signal to be transmitted on the transmission path, it is necessary to set an optimal value by determining the tap width and the intensity value (the modulation depth) for every tap. Further, there are two kinds of emphasis; the pre-emphasis in which when the emphasis is added, the signal is transmitted on the transmission path by adding the emphasis at a sender in advance so as to improve the waveform quality at a receiver; and the de-emphasis in which the emphasis is added immediately before the signal is received so as to improve the waveform quality immediately before the reception.
Furthermore, optimal setting values of the emphasis are different depending on applied systems. For this reason, in order to apply the emphasis, there are cumbersome works which involve setting respective parameters, searching for an optimal value of the emphasis while monitoring the waveform and the BER (Bit Error Rate), and setting the tap width and the intensity value (the modulation depth) for each tap.